Mica Minerals

Mica minerals make some rocks sparkle! They are often found in igneous rocks such as granite and metamorphic rocks such as schist. They sparkle because light is reflected on their flat surfaces, which are where the mineral breaks along its plane of cleavage. These minerals break so easily along their cleavage that some crystals have broken into many thin layers that look like the pages of a little book. Colonial Americans used the “pages” of large mica crystals as glass for windows.

The characteristics of the two most common types of mica are listed below. Notice how they are very similar in all ways except for their color? That is how you can tell them apart!

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TES XXVI, 3 fall 2010
The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

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